U.S. patent application number 14/563566 was filed with the patent office on 2015-06-11 for reactor for plasma-based atomic layer etching of materials.
The applicant listed for this patent is University of Maryland, College Park. Invention is credited to Dominik METZLER, Gottlieb S. OEHRLEIN.
Application Number | 20150162168 14/563566 |
Document ID | / |
Family ID | 53271880 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150162168 |
Kind Code |
A1 |
OEHRLEIN; Gottlieb S. ; et
al. |
June 11, 2015 |
REACTOR FOR PLASMA-BASED ATOMIC LAYER ETCHING OF MATERIALS
Abstract
Plasma-based atomic layer etching of materials may be of benefit
to various semiconductor manufacturing and related technologies.
For example, plasma-based atomic layer etching of materials may be
beneficial for adding and/or removing angstrom thick layers from a
surface in advanced semiconductor manufacturing and related
technologies that increasingly demand atomistic surface
engineering. A method may include depositing a controlled amount of
a chemical precursor on an unmodified surface layer of a substrate
to create a chemical precursor layer and a modified surface layer.
The method may also include selectively removing a portion of the
chemical precursor layer, a portion of the modified surface layer
and a controlled portion of the substrate. Further, the controlled
portion may be removed to a depth ranging from about 1/10 of an
angstrom to about 1 nm. Additionally, the deposition and selective
removal may be performed under a plasma environment.
Inventors: |
OEHRLEIN; Gottlieb S.;
(Clarksville, MD) ; METZLER; Dominik; (College
Park, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Maryland, College Park |
College Park |
MD |
US |
|
|
Family ID: |
53271880 |
Appl. No.: |
14/563566 |
Filed: |
December 8, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61913013 |
Dec 6, 2013 |
|
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Current U.S.
Class: |
438/694 ;
118/698; 156/345.25; 156/345.28; 216/37 |
Current CPC
Class: |
H01J 37/32082 20130101;
H01J 37/32146 20130101; H01L 21/31116 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01L 21/311 20060101 H01L021/311; C23C 16/455 20060101
C23C016/455; C23C 16/56 20060101 C23C016/56; C23C 16/52 20060101
C23C016/52 |
Claims
1. A method, comprising: depositing a controlled amount of a
chemical precursor on an unmodified surface layer of a substrate to
create a chemical precursor layer and a modified surface layer; and
selectively removing a portion of the chemical precursor layer, a
portion of the modified surface layer, and a controlled portion of
the substrate, wherein the controlled portion is removed to a depth
ranging from about 1/10 of an angstrom to about 1 nm, and wherein
the deposition and selective removal are performed under a plasma
environment.
2. The method of claim 1, further comprising cyclically repeating
the deposition of the controlled amount of the chemical precursor
and the selective removal of the portion of the chemical precursor
layer, the portion of the modified surface layer, and the
controlled portion of the substrate until a desired overall etching
depth is achieved.
3. The method of claim 1, further comprising controlling a rate of
removal of material in the selective removal process.
4. The method of claim 1, wherein the chemical precursor is
deposited in a plurality of pulse lengths using predetermined
amounts of time and mass flows, and wherein the selective removal
also accompanies the chemical precursor deposited in the
cycles.
5. The method of claim 4, wherein a thickness of the deposited
chemical precursor is about 1 angstrom to about 3 nm.
6. The method of claim 1, wherein the substrate comprises at least
one material that shows chemically induced etching in the presence
of low energy ion bombardment and the chemical precursor.
7. The method of claim 1, wherein the substrate comprises at least
one of SiO.sub.2, Si.sub.3N.sub.4, c-Si, amorphous Si,
poly-crystalline Si, Si.sub.xGe.sub.1-x, GaAs or other group III-V
semiconductors, GaAl.sub.xAs.sub.1-x, InGaAs.sub.1-x,
GaP.sub.xAs.sub.1-x, or the oxides, nitrides, or oxynitrides of the
above materials.
8. The method of claim 1, wherein the substrate comprises a native
oxide layer on the surface of the substrate, and wherein the native
oxide layer has a thickness of about 1/10 of 1 nm to about 10
nm.
9. The method of claim 1, wherein the substrate comprises high-k
dielectric films.
10. The method of claim 1, wherein the substrate comprises low-k
dielectric films, with or without nanopores.
11. The method of claim 9, wherein the substrate comprises at least
one of SiCOH, SiO.sub.yF.sub.x, or polymeric low-k dielectric
films, with or without nanopores.
12. The method of claim 9, wherein the high-k dielectric films
comprises Al.sub.2O.sub.3, HfO.sub.2, or Hf-silicate.
13. The method of claim 1, wherein the substrate comprises at least
one of graphene, graphite and other forms of carbon, deposited on a
Si or silicon-on-insulator substrate.
14. The method of claim 1, further comprising coupling a plasma
system to deposit the controlled amount of the chemical precursor,
and selectively remove the portion of the chemical precursor layer,
the portion of the modified surface layer, and the controlled
portion of the substrate.
15. The method of claim 1, further comprising applying a bias
potential to the substrate at a level configured to increase ion
energies, wherein the bias potential is synchronized to the
deposition of the controlled amount of the chemical precursor.
16. The method of claim 1, wherein the chemical precursor comprises
at least one of a hydrofluorocarbon C.sub.nF.sub.mH.sub.1, oxygen-,
or bromine-based gas.
17. The method of claim 16, wherein the chemical precursor
comprises fluorocarbon gas, and wherein the fluorocarbon gas
comprises at least one of the hydrofluorocarbon gas
C.sub.nF.sub.mH.sub.1 precursors or isomers thereof, or any
C.sub.nO.sub.mF.sub.1 gas precursors or isomers thereof, either
alone or with admixtures of either N.sub.2, H.sub.2, O.sub.2, CO,
CO.sub.2, noble gases, CH.sub.4, or SiF.sub.4, alone, or in
combination.
18. An apparatus, comprising: a coupled plasma system containing a
chemical precursor to be energized by the plasma and deposited on a
substrate; and a power source configured to supply a radio
frequency bias potential to the substrate, a controller configured
to control an amount of the chemical precursor applied to the
substrate to create a chemical precursor layer and a modified
surface layer, and the coupled plasma system and the power source
to selectively remove a portion of the chemical precursor layer, a
portion of the modified surface layer, and a controlled portion of
the substrate, wherein the controlled portion is removed to a depth
ranging from about 1/10 of an angstrom to about 1 nm, and wherein
the application of the chemical precursor and the selective removal
are performed under a plasma environment.
19. The apparatus of claim 18, wherein the controller is configured
to cyclically repeat the application of the amount of the chemical
precursor and the removal of the portion of the chemical precursor
layer, a portion of the modified surface layer, and the controlled
portion of the substrate until a desired overall etching depth is
achieved.
20. The apparatus of claim 18, wherein the controller is configured
to control a rate of removal in the selective removal process.
21. The apparatus of claim 18, wherein the chemical precursor is
deposited in a plurality of pulse lengths using predetermined
amounts of time and mass flows, and wherein the selective removal
also accompanies the chemical precursor deposited in the
cycles.
22. The apparatus of claim 21, wherein a thickness of the deposited
chemical precursor is about 1 angstrom to about 3 nm.
23. The apparatus of claim 18, wherein the substrate comprises at
least one material that shows chemically enhanced etching in the
presence of low energy ion bombardment and the chemical
precursor.
24. The apparatus of claim 18, wherein the substrate comprises at
least one of SiO.sub.2, Si.sub.3N.sub.4, c-Si, amorphous Si,
poly-crystalline Si, Si.sub.xGe.sub.1-x, GaAs or other group III-V
semiconductors, GaAl.sub.xAs.sub.1-x, InGaAs.sub.1-x,
GaP.sub.xAs.sub.1-x, X, or the oxides, nitrides, or oxynitrides of
the above materials.
25. The apparatus of claim 18, wherein the substrate comprises a
native oxide layer on the surface of the substrate, and wherein the
native oxide layer has a thickness of about 1/10 of 1 nm to about
10 nm.
26. The apparatus of claim 18, wherein the substrate comprises
high-k dielectric films.
27. The apparatus of claim 18, wherein the substrate comprises
low-k dielectric films, with or without nanopores.
28. The apparatus of claim 26, wherein the substrate comprises at
least one of SiCOH, SiO.sub.yF.sub.x, or polymeric low-k dielectric
films, with or without nanopores.
29. The apparatus of claim 26, wherein the high-k dielectric films
comprises Al.sub.2O.sub.3, HfO.sub.2, or Hf-silicate.
30. The apparatus of claim 18, wherein the substrate comprises at
least one of graphene, graphite and other forms of carbon,
deposited on a Si or silicon-on-insulator substrate.
31. The apparatus of claim 18, wherein the controller is configured
to control the coupled plasma system and the power source to remove
a further controlled portion of an unmodified portion of the
substrate.
32. The apparatus of claim 18, wherein the coupled plasma system
comprises at least one of an inductively coupled plasma system, a
capacitively coupled plasma system, an electron cyclotron resonance
plasma system, a Helicon wave plasma system, or an electron-beam
generated plasma system.
33. The apparatus of claim 18, wherein the chemical precursor
comprises at least one of a hydrofluorocarbon
C.sub.nF.sub.mH.sub.1, oxygen, or bromine gas.
34. The apparatus of claim 33, wherein the chemical precursor
comprises fluorocarbon gas, and wherein the fluorocarbon gas
comprises at least one of the hydrofluorocarbon gas
C.sub.nF.sub.mH.sub.1 precursors or isomers thereof, or any
C.sub.nO.sub.mF.sub.1 gas precursors or isomers thereof, either
alone or with admixtures of either N.sub.2, H.sub.2, O.sub.2, CO,
CO.sub.2, noble gases, CH.sub.4, or SiF.sub.4, alone, or in
combination.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to and claims the benefit and
priority of U.S. Provisional Patent Application No. 61/913,013,
filed Dec. 6, 2013, which is hereby incorporated by reference in
its entirety.
BACKGROUND
[0002] 1. Field
[0003] Plasma-based atomic layer etching of materials may be of
benefit to various semiconductor manufacturing and related
technologies. For example, plasma-based atomic layer etching of
materials may be beneficial for removing angstrom thick layers from
a surface in advanced semiconductor manufacturing and related
technologies that increasingly demand atomistic surface
engineering.
[0004] 2. Description of the Related Art
[0005] While atomic layer deposition has been tremendously
successful, the development of a corresponding atomic layer etching
(ALE) method has lagged. In atomic layer deposition, control of
deposited film thickness near one atomic monolayer may be based on
careful choice of chemical precursors which, once adsorbed at one
monolayer on the substrate, passivate the surface and prevent
multi-layer adsorption.
[0006] A subsequent reaction step transforms the precursor into the
desired material. Experimental and computational efforts aimed at
realizing a corresponding ALE approach using cyclic surface
passivation followed by removal of weakly bound chemical reaction
products resulting from interaction of the passivation layer with
the surface have been started in the past. These efforts have shown
that a key obstacle toward realizing ALE is achieving self-limited
etching, in particular for situations when ion bombardment to
remove the reacted material and precise control of surface coverage
by the chemical precursor is required.
[0007] Self-limited etching can require both negligible spontaneous
chemical etching by the precursor used to passivate the surface,
and insignificant physical sputtering of the unmodified material
after etch product removal. Minimizing physical sputtering has been
difficult to realize consistently, and additional factors, such as,
for example, photon-induced etching for plasma environments, have
also been invoked in an attempt to explain persistent etching for
certain conditions.
SUMMARY
[0008] According to certain embodiments, a method may include
depositing a controlled amount of a chemical precursor on an
unmodified surface layer of a substrate to create a chemical
precursor layer and a modified surface layer. The method may also
include selectively removing a portion of the chemical precursor
layer, a portion of the modified surface layer and a controlled
portion of the substrate. Further, the controlled portion may be
removed to a depth ranging from about 1/10 of an angstrom to about
1 nm. Additionally, the deposition and selective removal may be
performed under a plasma environment.
[0009] According to certain embodiments, an apparatus may include a
coupled plasma system containing a chemical precursor to be
energized by the plasma and deposited on a substrate. The apparatus
may also include a power source configured to supply a radio
frequency bias potential to the substrate. The apparatus may
further include a controller configured to control an amount of the
chemical precursor applied to the substrate to create a chemical
precursor layer and a modified surface layer, and the coupled
plasma system and the power source to selectively remove a portion
of the chemical precursor layer, a portion of the modified surface
layer and a controlled portion of the substrate. Further, the
controlled portion may be removed to a depth ranging from about
1/10 of an angstrom to about 1 nm. Additionally, the application of
the chemical precursor and the selective removal may be performed
under a plasma environment.
[0010] According to certain embodiments, an apparatus may include
means for depositing a controlled amount of a chemical precursor on
an unmodified surface layer of a substrate to create a chemical
precursor layer and a modified surface layer. The apparatus may
also include means for selectively removing a portion of the
chemical precursor layer, a portion of the modified surface layer
and a controlled portion of the substrate. Further, the controlled
portion may be removed to a depth ranging from about 1/10 of an
angstrom to about 1 nm. Additionally, the deposition and selective
removal may be performed under a plasma environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For proper understanding of the invention, reference should
be made to the accompanying drawings, wherein:
[0012] FIG. 1(a) illustrates real-time ellipsometry measurements
for selected conditions of an etching approach, according to
certain embodiments.
[0013] FIG. 1(b) illustrates the total etch depth of a polymer film
versus etching cycle number using the same conditions as in FIG.
1(a), according to certain embodiments.
[0014] FIG. 2 illustrates a thickness evolution during eight cycles
of a SiO.sub.2 ALE process, according to certain embodiments.
[0015] FIG. 3(a) illustrates thickness changes of fluorocarbon and
SiO.sub.2 during a single cycle of deposited fluorocarbon layer
with a C.sub.4F.sub.8 pulse time of 1.5 s, according to certain
embodiments.
[0016] FIG. 3(b) illustrates thickness changes of fluorocarbon and
SiO.sub.2 during a single cycle of deposited fluorocarbon layer
with a C.sub.4F.sub.8 pulse time of 3 s, according to certain
embodiments.
[0017] FIG. 4 illustrates XPS spectra comparing SiO.sub.2 with
thick 15 angstrom and thin 5 angstrom deposited fluorocarbon films
after various steps of the tenth ALE cycle, according to certain
embodiments.
[0018] FIGS. 5(a)-5(c) illustrate the variation of fluorocarbon
etching rates with fluorocarbon layer thickness and maximum ion
energy, according to certain embodiments.
[0019] FIGS. 5(d)-5(f) illustrate the variation of SiO.sub.2
etching rates with fluorocarbon layer thickness and maximum ion
energy, according to certain embodiments.
[0020] FIGS. 5(g)-5(i) illustrate the variation of SiO.sub.2
thickness removal, with fluorocarbon layer thickness and maximum
ion energy, according to certain embodiments.
[0021] FIG. 6 illustrates the dependency of fluorocarbon deposition
in each pulse on the amount of C.sub.4F.sub.8 admitted, according
to certain embodiments.
[0022] FIG. 7(a) illustrates deposition of fluorocarbon per cycle,
according to certain embodiments.
[0023] FIG. 7(b) illustrates removal of SiO.sub.2 per cycle,
according to certain embodiments.
[0024] FIG. 8 illustrates high control through a specialized
processing chamber with a small volume, temperate controlled
chambered walls, and time modulated power supply, according to
certain embodiments.
[0025] FIG. 9 illustrates a feed gas setup, according to certain
embodiments.
[0026] FIG. 10 illustrates a plasma based atomic layer etching
procedure, according to certain embodiments.
[0027] FIG. 11 illustrates a valve and power supply setup,
according to certain embodiments.
[0028] FIG. 12 illustrates a method according to certain
embodiments.
[0029] FIG. 13 illustrates a system according to certain
embodiments.
DETAILED DESCRIPTION
[0030] According to certain embodiments, it may be possible to
study and evaluate the use of cyclic plasma interacting with a
substrate. For example, cyclic Ar/C.sub.4F.sub.8 plasma interacting
with a substrate can be explored to determine for what conditions
controlled removal of substrate layers approaching one atomic layer
thickness per cycle can be achieved. Conditions for the removal of
substrate layers ranging from about 1/10 of an angstrom to about 1
nm can be achieved. In other embodiments, time-resolved surface
characterization can be implemented to confirm ALE.
[0031] The term atomic layer etching, as used herein, can broadly
refer to the level of layer dimensional control that can be
achieved at the angstrom level. Thus, atomic layer etching may
generally correspond to the size of atoms. Additionally, the
average removed layer thickness/cycle can be less than 1 angstrom
per etching cycle, or more than 1 angstrom/cycle.
[0032] Various substrates may be used in studying and evaluating
the use of cyclic plasma interacting with the substrate. For
example, such substrates may include materials that show chemically
enhanced etching in the presence of low energy bombardment and a
chemical precursor. The substrates can also include at least one of
SiO.sub.2, Si.sub.3N.sub.4, c-Si, amorphous Si, poly-crystalline
Si, Si.sub.xGe.sub.1-x, GaAs or other group III-V semiconductors,
GaAl.sub.xAs.sub.1-x, InGaAs, GaP.sub.xAs.sub.1-x, or the oxides,
nitrides, or oxynitrides of any of the above listed substrate
materials, or can be similar or like materials other than those
listed above. Additionally, the substrate may have a native oxide
layer on the surface of the substrate. Moreover, a thickness of the
native oxide layer may vary. For example, the thickness of the
native oxide layer may be about 1/10 of 1 nm to about 10 nm.
[0033] In other embodiments the substrate may also include high-k
dielectric films, or low-k dielectric films, with or without
nanopores. The high-k dielectric films may include Al.sub.2O.sub.3,
HfO.sub.2 or Hf-silicate. The low-k dielectric films may include at
least one of SiCOH, SiO.sub.yF.sub.x, or polymeric low-k dielectric
films, with or without nanopores. Moreover, in certain embodiments,
the substrate may further include at least one of graphene,
graphite and other forms of carbon, deposited on a Si or
silicon-on-insulator substrate. Additionally, the substrate may be
made up of a single material or a combination of materials arranged
in various formations such as, for example, stacks of multiple
materials.
[0034] The substrate, according to other embodiments, may include,
but are not limited to, wafers. The wafers may be of various
suitable processing sizes. For example, substrate samples may be on
the order of 1 inch or smaller, if desired. Additionally, full
wafers of about 200 mm or about 300 mm in diameter, or even larger
substrates may be incorporated.
[0035] The term substrate, as used herein, can broadly refer to any
layer upon which processing is desired. Thus, for example, a native
oxide film on the surface of a silicon substrate may itself be
considered a substrate for the purposes of this discussion.
Likewise, layers deposited on silicon or on other base substrates
may likewise be considered substrates in certain embodiments. For
example, in certain embodiments a multi-layer stack may be formed
and then atomic layer etching may be performed on the top layer of
the stack. In such a case, the top layer may be considered the
substrate. In general, the layer or layers upon which the chemical
precursor is deposited and/or which reacts with the chemical
precursor can be considered the substrate layer(s).
[0036] According to certain embodiments, angstrom thick precursor
layers can be used. For example, angstrom thick fluorocarbon (FC)
layers can be deposited to a thickness of about 1 angstrom to about
3 nm to form a modified SiO.sub.2 surface layer. The stoichiometry
of the FC layers is variable, and they may include other elements
not specifically called out, such as, for example, H. Subsequently,
after establishing a gaseous environment of sufficient purity, such
as, for example, by maintaining an Ar environment without
additional precursor injection, low energy Ar.sup.+ ion bombardment
can be applied to remove portions of the FC layer, portions of the
reacted SiO.sub.2 layer, and controlled portions of the SiO.sub.2
layer. This may be followed by another period during which an Ar
gaseous environment of sufficient purity is established. Such a
process can be repeated in a cyclical manner until a desired
overall etching depth has been achieved. Further, low energy ion
bombardment can be applied in various eV ranges, such as, for
example, within a range of about 0 eV up to about 100 eV. In other
embodiments, gases such as Ar, including Ne and/or Xe may also be
applied.
[0037] Material etching can stop once the reacted SiO.sub.2 surface
layer has been removed, resulting in a self-limited process. Thus,
according to certain embodiments, development of atomic layer
etching processes for complex materials may be feasible.
[0038] In other embodiments, various other precursors may be
applied in ALE. For example, other applicable precursors may
include oxygen gas and fluorocarbon gas, such as, for example,
C.sub.4F.sub.8, C.sub.4F.sub.6, or CF.sub.4. In further
embodiments, CHF.sub.3, any C.sub.nF.sub.mH.sub.1 or isomers
thereof, or any C.sub.nO.sub.mF.sub.1 gas or isomers thereof may be
applied. Additionally, Cl.sub.2 or at least one Br-based gas alone,
or in combination with fluorocarbon gases may also be applied.
Moreover, in other embodiments, the fluorocarbon gas may include at
least one of hydrofluorocarbon C.sub.nF.sub.mH.sub.1 gas precursors
or isomers thereof, or any C.sub.nO.sub.mF.sub.1 gas precursors or
isomers thereof, either alone or with admixtures of either N.sub.2,
H.sub.2, O.sub.2, CO, CO.sub.2, noble gases, CH.sub.4, or
SiF.sub.4, alone or in combination.
[0039] To realize FC layer deposition on the order of angstrom, a
pulsed FC injection into a low power Ar plasma may be used. For
example, in certain embodiments, a pulsed C.sub.4F.sub.8 injection
into a low power Ar plasma may be used. For an unbiased substrate,
precise FC film thickness control in the 1 angstrom to 3 nm range
may be possible by adjusting the total number N.sub.C4F8 of
C.sub.4F.sub.8 molecules entering the reactor of a plasma system by
varying pulse duration and C.sub.4F.sub.8 gas flow rate
appropriately. For these conditions, FC film thickness may increase
linearly with N.sub.C4F8.
[0040] To enable pulsed precursors with controlled, short pulse
times, a specialized tool configuration may be necessary. When the
pulse is injected into the processing chamber, the gas flow may be
redirected from a dump line into the chamber, allowing for precise
control of gas pulses, reactor pressure, and a stable flow
rate.
[0041] Following FC deposition, a small radio frequency (RF)
self-bias voltage may be applied for a predetermined amount of
time. For example, in certain embodiments, a small RF self-bias
voltage of -5, -10 and -15 V may be applied for 35 s. As a result,
maximum ion energies of 20, 25 and 30 eV, respectively, may be
created. For the low maximum ion energies, Ar.sup.+ ion induced
physical sputtering of unmodified SiO.sub.2 may be negligible. At
the end of a cycle, the process sequence may be repeated to achieve
precise control over the total etched thickness.
[0042] According to other embodiments, controlled, self-limited
etching of a polystyrene polymer using a composite etching cycle
may be performed. In such embodiments, each etching cycle may
consist of multiple steps. For example, in a first step, a modified
surface may be produced by exposing the polymer surface to O.sub.2.
The oxygen may be adsorbed on the surface and form a reactive
layer, especially if the polymer has already been modified by ion
bombardment. Subsequently, in a second step, low-pressure Ar plasma
etching may remove the oxygen-modified deposited reactive layer
along with various amounts of the unmodified polymer, such as, for
example, approximately 0.1 nm unmodified polymer.
[0043] Moreover, in certain embodiments, an optical multilayer
model may be used to extract the film thickness and complex index
of refraction in real-time using in situ ellipsometry. The total
etched thickness may increase linearly with the number of ALE
cycles due to a roughly constant removed thickness per cycle.
Excellent reproducibility and nearly constant etching depth per
cycle is shown for twenty cycles, for example, in FIGS. 1(a) and
1(b), according to certain embodiments. Specifically, FIG. 1(a)
illustrates real-time ellipsometry measurements for selected
conditions of the etching approach, and FIG. 1(b) illustrates total
etch depth of a polymer film versus etching cycle number using the
same conditions as in FIG. 1(a).
[0044] To carry out ALE procedures, according to certain
embodiments, various plasma system may be used. For example in
certain embodiments, an inductively coupled plasma system may be
used. In other embodiments, the plasma system may include
capacitively coupled plasma systems, electron cyclotron resonance
plasma systems, Helicon wave plasma systems, and electron-beam
generated plasma systems. The plasma systems may also include
magnetic enhancements and controllers configured to control an
amount of chemical precursor deposition, and control the removal of
portions of the chemical precursor layer(s), modified surface
layer(s), and controlled portion of the substrate.
[0045] The plasma system may be excited at various frequencies,
both high and low. For example, according to certain embodiments,
the plasma system may be excited at 13.56 MHz. The base pressure
achieved before processing may be in various ranges, such as, for
example, the 1.times.10.sup.-6 Torr range, and the temperature of
the samples may be stabilized by substrate cooling during plasma
processing.
[0046] Various materials may also be used with the plasma system.
For example, SiO.sub.2--Si--SiO.sub.2 stacks deposited on an Si
substrate may be used. The SiO.sub.2--Si--SiO.sub.2 stacks may be
deposited on the Si substrate by plasma-enhanced chemical vapor
deposition (PECVD) techniques and studied by in-situ ellipsometry
in real time. In other embodiments, the various substrate materials
described above may also be used.
[0047] Controlled deposition and chemical modification of the
surface may allow selective removal of a sub-nm layer of SiO.sub.2,
where selective removal may be represented in terms of the material
that is removed under the precursor layer, which has been modified,
or is modified during the removal process. To establish
strongly-time-dependent etch rates, a sequential approach may be
used consisting of a thin FC layer deposition followed by a low
energy Ar.sup.+ ion etch for selective removal of volatile
material.
[0048] FIG. 2 illustrates a thickness evolution for an SiO.sub.2
layer for multiple cycles, along with the process parameters of one
cycle, according to certain embodiments. At the beginning of each
cycle, a pulse of C.sub.4F.sub.8 may be injected for 1.5 s into a
continuous argon plasma, and deposits about 5 angstrom of FC film.
A synchronized RF bias potential may be applied to the substrate 8
s after the C.sub.4F.sub.8 pulse to increase Ar.sup.+ ion
bombardment energies. This initiates FC film etching, and etching
of the modified surface layer, followed by strongly time-dependent
SiO.sub.2 etching.
[0049] Etching or removal of the FC film and the modified surface
layer, along with a controlled portion of the SiO.sub.2 substrate
may be uniform. For example, in certain embodiments, the surface
roughness of FC layer, modified surface layer, layers of the
SiO.sub.2 may remain unchanged during etching.
[0050] FIG. 2 also illustrates that the initially high SiO.sub.2
etch rate continuously decreases and finally ceases. The
ion-induced reaction of deposited FC with SiO.sub.2 may enable
transient etching and controlled removal of an ultra-thin SiO.sub.2
layer. Each cycle shows a similar behavior, although there are
small systematic differences which will be further discussed
below.
[0051] FIG. 2 further illustrates that the approach permits a high
degree of control over total etched SiO.sub.2 thickness. For
instance, for Ar.sup.+ ion energies of 20 eV, ion-induced removal
of chemical reaction products may dominate etching, and unmodified
SiO.sub.2 may etch at a negligible rate.
[0052] According to certain embodiments, etching of SiO.sub.2 for
low energy ion conditions may be dominated by the fluorocarbon
reactants and may result in an etch rate decrease with time until
the initially deposited FC layer is depleted and etching ceases.
This effect can be seen in the expanded views of single etching
cycles for two conditions, as illustrated in FIGS. 3(a) and 3(b),
according to certain embodiments.
[0053] FIGS. 3(a) and 3(b) illustrate thickness changes of
fluorocarbon and SiO.sub.2 during a single cycle for two
thicknesses of deposited FC layer achieved by changing the
C.sub.4F.sub.8 pulse time from 1.5 s to 3 s, respectively. In FIG.
3(a), after deposition of 5 angstroms of FC, a bias potential of
-10 V was applied. According to certain embodiments, the bias power
may be supplied to a bottom electrode, which controls ion energies,
and may be shut off during C.sub.4F.sub.8 injection. The low energy
ions induce etching of the FC layer and additionally reaction of
carbon and fluorine with the underlying SiO.sub.2. The resulting
modified SiO.sub.2 surface layer was etched by low energy Ar.sup.+
ion bombardment until the modified layer has been removed, when
SiO.sub.2 etching ceases. As shown in FIG. 3(b), a similar change
in etch rate over time can be observed upon deposition of a thicker
FC layer on SiO.sub.2.
[0054] In certain embodiments, a steady-state may not be reached
within the period the RF bias is applied. Therefore, even at the
end of the etching cycle, FC material may still be present at the
SiO.sub.2 surface and enable a finite etch rate. This can be
minimized by using shorter C.sub.4F.sub.8 pulses.
[0055] Precise admission of chemical reactants to the system can be
an important factor in ALE. As such, it may be expected that
residual FC deposited on the chamber walls may interfere with the
management of chemical reactant supply at the substrate surface and
reduce control over the etching process. For instance, FIG. 2 shows
that the time-dependent etch rate during the second half of each
cycle increases slightly from cycle to cycle. Residual FC entering
the gas phase from the chamber walls between C.sub.4F.sub.8 pulses
can redeposit on the exposed, unmodified SiO.sub.2 and increase
SiO.sub.2 etching for FC reactant-starved process conditions in the
later part of a cycle. Thus, maintaining a well-defined clean
process chamber conditions to control supply of chemical reactants
may be important for achieving ALE processes in a plasma reactor.
Heating of the interior surfaces of the apparatus that surround the
substrate along with additional pumping during periods with no bias
to the substrate can improve chamber cleanliness and process
control.
[0056] According to certain embodiments, to obtain insights on
changes in surface chemistry throughout one cycle, X-ray
photoelectron spectroscopy (XPS) may be performed after the FC
deposition step, during the SiO.sub.2 etch step, and after
completion of a cycle. To study steady-state conditions,
experiments were performed for the tenth cycle of a sequence. The
results are shown in FIGS. 4(a) and 4(b), which summarize the
different binding energy regions of interest (Si 2 p, C 1 s, O 1 s,
and F 1 s).
[0057] Data are shown for 15 angstrom and 5 angstrom thick FC films
in FIGS. 4(a) and 4(b), respectively. Si 2 p and O 1 s spectra were
fit using SiO.sub.2 and SiOF at 103.9 eV and 104.1 eV, and 533.2 eV
and 533.4 eV, respectively. C 1 s spectra were fit using C--C/H,
C--CF.sub.x, CF, CF.sub.2, and CF.sub.3 peaks at 285 eV, 287 eV,
289.1 eV, 291.2 eV, and 293.4 eV, respectively. F 1 s spectra were
fit using SiF.sub.x, CF, and CF.sub.2 at 687.8 eV, 686.9 eV and 689
eV, respectively.
[0058] According to certain embodiments, a reduction in F content
can be seen throughout the etch step for a deposited film of 15
angstroms, as illustrated in FIG. 4. The C 1 s spectra show a
reduction in carbon-bonded fluorine. The Si 2 p and O 1 s signals
increase correspondingly since they originate from the SiO.sub.2
underneath the FC film. FIG. 4 also illustrates an SiO.sub.2
surface covered with a thin FC film of 5 angstroms, according to
certain embodiments. In particular, FIG. 4 shows little of the
characteristic fluorocarbon bonding signature in the C 1 s spectrum
and only a slight F 1 s signal reduction after etching in contrast
to samples covered with a thick FC film. Since the C 1 s spectrum
shows the same reduction of carbon bonded to fluorine as the
thicker films, the remaining fluorine must be associated with
SiO.sub.2. Bonding of fluorine with SiO.sub.2 is shown by a slight
shift of the Si 2 p and O 1 s spectra towards higher binding
energy, consistent with the more electronegative environment.
[0059] According to certain embodiments, the FC layer may play a
critical role in enabling SiO.sub.2 etching for the low energy ion
bombardment conditions used. FIGS. 5(a)-5(c) summarize the
variation of FC etching rates, FIGS. 5(d)-5(f) summarize the
variation of SiO.sub.2 etching rates, and FIGS. 5(g)-5(i) summarize
the variation of SiO.sub.2 thickness removal, with FC layer
thickness and maximum ion energy. The time dependent etch rate
within one cycle increases with FC film thickness and maximum
Ar.sup.+ ion energy.
[0060] Once a critical FC layer thickness on SiO.sub.2 is reached,
the FC reaction with SiO.sub.2 no longer increases with FC film
thickness, and SiO.sub.2 etched per cycle may saturate. If the FC
layer thickness exceeds this critical thickness, on the order of
the projected range of Ar.sup.+ ions in the FC material, the
additional FC deposited may be etched by Ar.sup.+ bombardment with
little interaction with the SiO.sub.2 underneath.
[0061] The impact of FC film thickness on SiO.sub.2 etch rate may
be seen in FIGS. 5(d), 5(e) and 5(f), which show an increase with
both FC layer thickness and maximum ion energy. The maximum
SiO.sub.2 etch rate is not a strong function of total FC film
thickness above 5 angstroms, but the minimum SiO.sub.2 etch rate
(achieved at the end of the cycle), depends strongly on FC film
thickness. A deposited FC film thickness of 4 angstroms or less is
required to achieve minimal SiO.sub.2 etching at the end of the
cycle at the low ion energies. FIGS. 5(a) to 5(i) show that the
SiO.sub.2 etch rate and SiO.sub.2 thickness removed per etching
cycle increase with maximum Ar.sup.+ ion energy for a given FC
layer thickness.
[0062] According to certain embodiments, using a steady-state Ar
plasma, periodic injection of a defined number of C.sub.4F.sub.8
molecules and synchronized plasma-based Ar.sup.+ ion bombardment,
atomic layer etching of SiO.sub.2 is possible. The thickness of a
deposited FC layer in the range of 1 angstrom to 3 nm, and Ar.sup.+
ion bombardment may be used to control the chemical modification of
SiO.sub.2, thus enabling etching of SiO.sub.2 for low energy ion
bombardment conditions for which the physical sputter rate of
SiO.sub.2 is negligible. In other embodiments it may be possible to
measure the enhancement of the SiO.sub.2 etch rate relative to the
physical sputter rate at Ar.sup.+ ion energies below 30 eV as a
function of FC surface coverage. Results are consistent with
computational simulations that first suggested the feasibility to
achieve ALE for the fluorocarbon/Ar.sup.+/SiO.sub.2 system.
[0063] In order to control the deposited FC layer thickness, the
C.sub.4F.sub.8 pulse length and flow rate may be adjusted. Longer
pulses and/or higher flows admit more C.sub.4F.sub.8 molecules into
the chamber, which may create a thicker FC layer.
[0064] FIG. 6 illustrates how the FC thickness depends linearly on
the admitted amount of C.sub.4F.sub.8 in this regime of short
pulses and low flows, according to certain embodiments. If the
pressure in the dump line is significantly higher than the
processing pressure, large amounts of precursor may be admitted to
the chamber at the beginning of the pulse. The pressure in the dump
line system can be adjusted by regulating the pump speed via a leak
valve. In certain embodiments, the dump line system pressure may be
adjusted to be similar to the processing pressure.
[0065] FIGS. 7(a) and 7(b) illustrate the influence of deposited FC
layer thickness on SiO.sub.2 etch rate at pulses of 1.5 s and 3.0
s, while the Ar ion bombardment time is 35 s in both cases,
according to certain embodiments. In FIG. 7(a), thickness evolution
of FC is shown during several cycles for two selected conditions of
different pulse lengths and times in between consecutive pulses.
Here, pristine SiO.sub.2 cannot be etched with a pure Ar plasma at
the low source powers and ion energies used. Thin FC film
deposition can enable low energy ion etching of SiO.sub.2. When
admitting C.sub.4F.sub.8 to the processing chamber, a thin FC layer
can be deposited until the precursor is depleted. The thin
additional layer that may be removed as precursor from the
precursor layer may be brought into contact with previously
unreacted substrate, reacted, and then immediately removed.
Subsequently, a bias power may be applied to the substrate to
increase the ion energies. With the applied bias, the FC layer
together with a thin SiO.sub.2 layer may be rapidly etched.
[0066] The etch rate may decrease as the FC layer is removed
together with a thin layer of SiO.sub.2. Once the FC layer is fully
removed, the etching ceases. Additionally, some negligible amount
of unmodified substrate may be removed even without reacting with
the precursor, as mentioned above. Subsequently, the next pulse
deposits a new FC layer repeating the process. More specific
effects are shown in FIG. 7(b), which show the removal of SiO.sub.2
per pulse.
[0067] According to certain embodiments, time dependent modulation
of various parameters and plasma properties may be necessary for
high process control. Moreover, FIG. 8 illustrates that high
control can be achieved through a feed gas setup and a specialized
processing chamber with, for example, a small volume, temperature
controlled inner surfaces of chamber walls, and time modulated
power supply, according to certain embodiments.
[0068] FIG. 9 illustrates a possible feed gas setup enabling short,
controlled precursor pulses, according to certain embodiments. In
particular, the feed gas setup shows various gas lines with
multiple valves and mass flow controllers (MFC) leading up to a
line to the processing chamber, and a dump line to a pump.
[0069] FIG. 10 illustrates a plasma based atomic layer etching
procedure, according to certain embodiments. In particular,
according to FIG. 10, plasma based atomic layer etching may require
great control over the precursor admission to the processing
chamber, ion energies, and chamber condition. In certain
embodiments, the cyclic approach may deposit a thin film enabling
low energy ions to subsequently remove the topmost layer without a
significant unmodified material etch.
[0070] FIG. 11 illustrates a valve and power supply setup,
according to certain embodiments. In particular, lines A and B can
both be independently activated as necessary. The source and bias
power can also be activated as needed. Further, each time can be
chosen according to the processing parameters to allow maximum
flexibility. Additional possible delays can also be
implemented.
[0071] FIG. 12 illustrates a method according to certain
embodiments. As shown in FIG. 12, a method may include, at 110,
coupling a plasma system to deposit the controlled amount of the
chemical precursor. The method may also include, at 120, depositing
a controlled amount of a chemical precursor on an unmodified
surface layer of a substrate to create a chemical precursor layer
and a modified surface layer. The method may further include, at
130, establishing a gaseous environment of sufficient purity. In
certain embodiments, this can be done by maintaining an Ar
environment without additional precursor injection. The method may
also include, at 140, controlling a rate of selectively removing
the portion of the chemical precursor layer, the portion of the
modified surface layer, and the controlled portion of the
substrate.
[0072] The method may also include, at 150, applying a bias
potential to the substrate at a level configured to increase ion
energies. The method may further include, at 160, selectively
removing a portion of the chemical precursor layer, a portion of
the modified surface layer, and a controlled portion of the
substrate in a cyclical process. The method may also include, at
170, again establishing an Ar gaseous environment of sufficient
purity. Once an Ar gaseous environment of sufficient purity is
again established, the method may be repeated as a cyclical process
beginning again from 120 until a desired overall etching depth is
achieved. If desired, variations on pulse length and precursor
thickness can vary from cycle to cycle. Thus, it is not required
that all cycles be identical. However, in certain embodiments, the
cycles may be identical if desired.
[0073] FIG. 13 illustrates a system according to certain
embodiments. In one embodiment, a system may include a coupled
plasma system 240. The coupled plasma system 240 may be any plasma
system mentioned above. The system may also include a power source
250. The power source 250 may be configured to supply a radio
frequency bias potential to the substrate.
[0074] The system may also include a controller 210 that is
connected to the coupled plasma system 240. The controller 210 may
be configured to control an amount of the chemical precursor to be
applied to the substrate, and also control the selective removal of
portions of the chemical precursor layer, the modified surface
layer, and the controlled portion of the substrate.
[0075] The controller 210 may include at least one processor 220.
At least one memory 230 may be provided in the controller 210. The
memory 230 may include computer program instructions or computer
code contained therein. Other configurations of the controller 210
may also be provided.
[0076] The processor 220 may be a single or multiple core central
processing unit (CPU). Memory 230 may be any suitable storage
device, such as a non-transitory computer-readable medium. A hard
disk drive (HDD), random access memory (RAM), flash memory, or
other suitable memory may be used. Furthermore, the computer
program instructions may be stored in the memory 230 and which may
be processed by the processor 220 can be any suitable form of
computer program code, for example, a compiled or interpreted
computer program written in any suitable programming language. The
memory or data storage entity is typically internal but may also be
external or a combination thereof, such as in the case when
additional memory capacity is obtained from a service provider.
[0077] The memory 230 and the computer program instructions may be
configured, with the processor 220 for the particular device, to
cause a hardware apparatus such as controller 210, to perform any
of the processes described above (see, for example, FIG. 15).
Therefore, in certain embodiments, a non-transitory
computer-readable medium may be encoded with computer instructions
or one or more computer program (such as added or updated software
routine, applet or macro) that, when executed in hardware, may
perform a process such as one of the processes described herein.
Computer programs may be coded by a programming language, which may
be a high-level programming language, such as objective-C, C, C++,
C#, Java, etc., or a low-level programming language, such as a
machine language, or assembler.
[0078] One having ordinary skill in the art will readily understand
that the invention as discussed above may be practiced with steps
in a different order, and/or where each individual step may be
varied to achieve optimal performance of the overall process,
and/or with hardware elements in configurations which are different
than those which are disclosed. Therefore, although the invention
has been described based upon these preferred embodiments, it would
be apparent to those of skill in the art that certain
modifications, variations, and alternative constructions would be
apparent, while remaining within the spirit and scope of the
invention. In order to determine the metes and bounds of the
invention, therefore, reference should be made to the appended
claims.
[0079] Glossary
[0080] ALE Atomic Layer Etching
[0081] CPU Central Processing Unit
[0082] FC Fluorocarbon
[0083] HDD Hard Disk Drive
[0084] MD Molecular Dynamics
[0085] MFC Mass Flow Controller
[0086] PECVD Plasma-enhanced Chemical Vapor Deposition
[0087] RAM Random Access Memory
[0088] RF Radio Frequency
[0089] XPS X-Ray Photoelectron Spectroscopy
* * * * *